Cocaine receptor binding ligands

ABSTRACT

Tropane derivatives having a high binding affinity and selectivity for dopamine transporters bear, on the tropane backbone either a carboxylic ester or isoxazole moiety, as well as a substituted phenyl moiety. The compounds have utility both as pharmaceutical and as imaging agents, when one or more atoms are radioactive.

PARENT APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patent application Ser. No. 08/436,970 and U.S. patent application Ser. No. 08/164,576. The latter application is in turn a continuation-in-part application of U.S. patent application Ser. No. 07/792,648, now U.S. Pat. No. 5,380,848, which is in turn a continuation-in-part of U.S. patent application Ser. No. 07/564,755, filed Aug. 9, 1990, now U.S. Pat. No. 5,128,118 and U.S. patent application Ser. No. 07/972,472, based on U.S. PCT Application PCT/US91/05553, filed Aug. 9, 1991, now U.S. Pat. No. 5,413,979. The entire of disclosure of U.S. patent application Ser. No. 08/164,576 and U.S. Pat. Nos. 5,413,779, 5,380,848 and 5,128,118 are incorporated herein by reference.

THE INVENTORS' PRIOR DISCLOSURES

[0002] The parent applications referenced above are directed to cocaine receptor binding ligands, which show enhanced affinity for binding to cocaine receptors, particularly dopamine transporter sites, although binding affinity is also high at serotonin transporters. These prior patents and patent applications are directed to compounds having the general formula:

[0003] Wherein Y=CH₂R₃, CO₂R₂, CONRR¹, or

[0004] R₁=hydrogen, C₁₋₅ alkyl,

[0005] R₂=hydrogen, C₁₋₆ alkyl, C₃₋₈ cycloalkyl, C₁₋₄ alkoxy, C₁₋₆ alkynyl, halogen or amine,

[0006] R₃=OH, hydrogen, C₁₋₆ alkyl, C₃₋₈ cycloalkyl, C₁₋₄ alkoxy, Cl, Br, I, CN, NH₂, NHC₁₋₆ alkyl, NC₁₋₆ alkyl, OCOC₁₋₆ alkyl OCOC₁₋₃ alkylaryl,

[0007] A=S, O or N

[0008] X=H, C₁₋₆ alkyl, C₃₋₈ cycloalkyl, C₁₋₄ alkoxy, C₁₋₆ alkynyl, halogen, amino acylamido, and

[0009] Z=H, I, Br, Cl, F, CN, CF₃NO₂, N₃, OR₁, CO₂NH₂, CO₂R₁, C₁₋₆ alkyl, NR₄R_(5,) NHCOF₅, NHCO₂R₆

[0010] wherein R₄-R₆ are each C₁₋₆ alkyl, R and R¹ are independently H, C₁₋₆ alkyl, C₁₋₆ alkene, C₁₋₆ alkyne, phenyl, phenyl substituted with 1-3 of C₁₋₆ alkyl, alkene, alkyl or alkoxy, C₁₋₆ alkoxy, phenoxy, amine, amine substituted with 1-2 of C₁₋₆ alkyl, alkene, alkyne, alkoxy or phenyl or phenoxy or R and R¹ may combine to form heterocyclic structure including pyrrolidinyl, piperidinyl and morpholino moieties, unsubstituted or substituted with 1-2 C₁₋₆ alkyl, alkene, alkyne or alkoxy groups.

[0011] As is reflected in the parent applications and patents, due to the high binding affinity of these compounds, particularly as measured against the compound of the literature [³H]WIN 35,428 binding inhibition, these compounds have found particular use in both positron emission tomography (PET) as well as single photon emission computed tomography (SPECT). For PET use, one of the carbons of the molecule should be an [¹¹C] labeled form, while SPECT imaging may employ a radioactive halogen label, such as the molecule on the phenyl ring of the general formula, either X or Z of the above-described general formula. In particular, the radioactive labels ¹²³I, ¹²⁵I and ¹³¹I may be used.

[0012] As this art has developed, it has proved difficult to determine what particular substitutions on the tropane backbone will yield high binding affinities while remaining pharmaceutically acceptable. The applicant has now discovered a new family of tropane derivatives, characterized by an aryl ring substituent, and either an isoxazole substituent or a carboxylic ester substituent. These particular compounds have been demonstrated to have a high dopamine transporter binding efficiency, and a high selectivity.

SUMMMARY OF THE INVENTION

[0013] Compounds of the general formula:

[0014] Wherein

[0015] R₁ is hydrogen, C₁₋₅ alkyl

[0016] R_(a) is phenyl, C₁₋₆ alkyl, C₁₋₆ alkyl-substituted phenyl

[0017] R_(b) is C₁₋₆ alkyl, phenyl, C₁₋₆ alkyl substituted phenyl and

[0018] Z is phenyl or naphtyl bearing 1-3 substituents selected from the group consisting of F, Cl, I, C₁₋₆ alkyl, each substituent may be or include a radioactive label, fall within the scope of this invention.

[0019] These compounds have been demonstrated to have particular high binding affinity and selectivity for dopamine transporter sites.

[0020] The compounds of the invention can be prepared according to the methodologies established in the parent applications, incorporated herein by reference. The method of making the compound, per se, does not constitute an aspect of the invention. Particular measures for preparation of the isoxazole derivatives are shown herein. Nonetheless, other methods of making the compounds will occur to those of ordinary skill in the art, without the exercise of inventive faculty.

[0021] 3β-(4′-Chlorophenyl)-2β-(3′-phenylisoxazol-5-yl)tropane) (4,RTI-177)Hydrochloride

[0022] A soloution of n-butyl lithium in hexane (2.4M, 4.2 mL, 10.4 mmol) was added to a stirred solution of acetophenone oxime (0.703 g, 5.2 mmol) in a dry THF (10 mL) at 0° C. under nitrogen. After 1 h, a soloution of 3β-(4-chlorophenyl)tropane-2β-carboxylic acid methyl ester (1.18 g, 4 mmol) in dry THF (8 mL) was added, and the solution was allowed to warm to room temperature over 18 h. The mixture was poured into a stirred solution of concentrated sulfuric acid (2.28 g) in THF (12 mL) and water (2.8 mL) and was heated under reflux for 1 h. The cooled solution was basified using saturated aqueous potassium carbonate (10 mL) and extracted with 3×10 mL methylene chloride. The combined organic layer was dired and filtered. Removal of solvent under vacuum gave 1.46 g solid. Purification of the solid by flash column chromatography [20% (ether:triethylamine 9:1) in hexane] gave 0.75 g (50%) of pure 4 which was further purified by recrystallizing from ether:petroleum ether. ¹H NMR (CDCl₃) §1.74(m,3), 2.22 (m,3), 2.27 (s,3), 3.24 (m,2), 3.36 (m,2), 6.80 (s.1), 6.94 (m,2), 7.12 (m,2), 7.40 (m,3), 7.76 (m,2). IR (CHCl₃)2940, 1600, 1590, 1490, 1405, 1350 cm⁻¹.

[0023] The hydrochloride salt had mp 287° C. (dec); [α² _(D3) −97.5 (c 0.28, CH₃OH). ¹H NMR (CH₃OD) α 2.35 (m,6), 2.84 (s,3), 3.73 (m,1), 4.09 (m,1), 4.21 (m,1), 6.12 (s,1), 7.14 (m,4), 7.34 (m,3), 7.57 (m,2).

[0024] Anal. Calcd for C₂₃H₂₄Cl₂N₂0.0.25H₂O: C,H,N.

[0025] 3α-(4′-Chlorophenyl)-2α-(5′-phenyl-1′,3′,4′-oxadiazol-2′-yl)tropane(5,RTI-188) Hydrochloride

[0026] To 0.59 g (2 mmol) of 8 in 2 mL of POCl₃ was added 1.1 eq. of benzoic hydrazide, and the solution was reluxed under N₂ for 2 h. The reaction miscture was cooled and poured into ice and basified to pH 7-8 using conc. NH₄OH. To the aqueous layer was added 10 mL brince followed by extraction with 3×10 mL methylene chloride. The combined organic layer was dried (NaSO₄), filtered, andthe solvent removed in vacuo to give 0.9 g residue. PUrification of this residue by flash column chromatography [50% (ether:triethylamine 9:1) in hexane gave 0.33 g (42%) of pure 5 which was recrystallized from ether:petroleum ether.

[0027] Well-established protocols for determining binding efficiency have shown selected compounds, pictured below, to have particularly high binding affinity, and selectivity, for dopamine transporter sites.

Comparison of Transporter Binding Potencies for Selected 3β-(4-Substituted Phenyl)tropan-2β-carboxylic Acid Methyl Esters

IC₅₀(nM) DA NE 5-HT NE/DA 5-HT/DA RTI No. X Y [³H]WIN 35,428 [³H]Nisoxetine [³H]Paroxetine Ratio Ratio WIN 35,065-2 H H 23 920 1962 40 85 WIN 35,428 F H 13.9 835 692 60 50 RTI-32 CH₃ H 1.71 60 240 35 140 RTI-31 Cl H 1.12 37 44.5 33 40 RTI-55 I H 1.26 36 4.21 29 3.3 RTI-51 Br H 1.69 37.4 10.6 22 6 RTI-88 NH₂ I 1.35 1329 120 984 89 RTI-111 Cl Cl 0.79 17.96 3.13 67 4 RTI-112 Cl CH₃ 0.81 36.2 10.5 45 13 RTI-318

0.51 21.1 0.80 41 1.6

[0028] 3β-(4′-Methylphenyl)-2β-(heterocyclic)tropane

IC₅₀(nM) DA NE 5-HT NE/DA 5-HT/DA RTI No. Het [³H]WIN 35,428 [³H]Nisoxetine [³H]Paroxetine Ratio Ratio 151

2.33 60 1074 26 461 171

0.93 254 3818 273 410 176

1.58 398 5110 252 3234 178

35.4 677 1699 19 48 194

4.45 253 4885 57 1098 195

47.48 1310 22,310 28 470 199

35.88 24,320 51,460 678 1434

[0029] 3β-(4′-Chlorophenyl)-2β-(heterocyclic)tropanes

IC₅₀(nM) RTI DA NE 5-HT NE/DA 5-HT/DA No. Het [³H]WIN 35,428 [³H]Nisoxetine [³H]Paroxetine Ratio Ratio 130

1.62 244.6 195 151 120 188

12.6 930 3304 74 262 200

15.3 4142 18,416 271 1203 165

0.59 181 572 307 970 177

1.28 504 2418 394 1889 189

19.7 496 1116 25 57 219

5.71 8563 10,342 1500 1811 202

1.37 403 1119 294 817

IC₅₀(nM) IC₅₀(nM) DA 5-HT NE DA 5-HT NE 14 156 85 0.51 0.80 21

IC₅₀(nM) IC₅₀(nM) DA 5-HT NE DA 5-HT NE 21 5062 1231 1.1 11.4 70.2

[0030] It should be noted that the compounds described and claimed herein are not useful solely as imaging compounds. The compounds are useful as surrogate agonists for treatment of cocaine abuse, as well as abuse of other psychostimulant drugs including amphetamines. The compounds of this invention exhibit a very slow onset of action, as well as a very long duration of action. Both of these attributes are desirable for appropriate substitute medication for psychostimulant abuse.

[0031] These compounds, because of their selectivity for the dopamine transporter are useful as antagonist drugs, or blockers of the actions of cocaine or other psychostimulants, blocking psychostimulant access but not inhibiting the functioning of the transporter. Further, treatment of neurodegenerative disorders may be affected through potentiation of neurotransmitter action. The compounds of the invention may be used to inhibit re-uptake in such situations. Finally, these compounds may find utility as analgesics. Accordingly, the compounds have utility in both their labeled and unlabeled forms.

[0032] This invention has been disclosed in terms of generic formula, as well as by specific example. Where examples are set forth, they are not intended, and should not be interpreted, as limiting. In particular, isomeric forms, as well as alternate substituents will occur to those of ordinary skill in the art without the exercise of inventive faculty, and remain within the scope of the invention, which is unlimited save by the recitation of the claims below. 

What is claimed is:
 1. A binding ligand having high binding affinity and selectivity for dopamine transporters, having the formula

Wherein R₁ is hydrogen, C₁₋₅ alkyl R_(a) is phenyl, C₁₋₆ alkyl, C₁₋₆ alkyl-substituted phenyl R_(b) is C₁₋₆ alkyl, phenyl, C₁₋₆ alkyl substituted phenyl and Z is phenyl or naphtyl bearing 1-3 substituents selected from the group consisting of F, Cl, I, C₁₋₆ alkyl, each substituent may be or include a radioactive label, fall within the scope of this invention.
 2. The binding ligand of claim 1, wherein said compound is of one of the following formulas:


3. The binding ligand of claim 1, wherein said binding ligand bears a radioactive molecule selected from the group consisting ^(of 11)C, ¹²³I, ¹²⁵I, ¹³¹I. 